Cardiff Blues forward Michael Paterson is facing three weeks on the sidelines after breaking a bone in his foot.
The New Zealander has fractured his sesamoid, a small bone beneath the big toe, and will now miss the Magners League clash with Aironi as well as the last two rounds of Heineken Cup action.
"After the Northampton game I had a scan and it showed a fracture of the sesamoid. I have no idea when I did it, it could have been a pressure thing at the scrum, or in a tackle, I just don't know," Paterson told the official Magners League's site.
"It's just a case of resting up and letting it heal by itself. Obviously that means I'm restricted training wise but I'm keeping busy in the gym and doing a lot of work in the pool.
"I'm ruled out but this game is of huge importance to us. Hopefully we can bounce on from the win last weekend and play the way we did in the first half. In the second half we fell off for a bit so it's vital that we get back to that first-half performance.
"We can't underestimate them and we will worry about the win first - if we can get the bonus-point then that's a plus."